There is an ongoing need for providing novel improved electrical storage batteries, which are low-cost have a high-energy density and are environmentally acceptable. Among the main types of storage batteries are those in which the cathodes (the positive electrodes) are based on any of PbO.sub.2, HgO, MnO.sub.2 and NiOOH which are known to possess a theoretical capacity in the range of between 224 to 308 Ah/g. However, these cathode materials are considered as hazardous or environmentally unfriendly.
In a very recent U.S. Pat. No. 5,429,894, iron-silver (iron in its zero valence state) was suggested as a battery anode (negative). Iron salts in the +2 and +3 valence state, were also suggested as a battery cathode in the past as described, for example, in U.S. Pat. No. 4,675,256 and U.S. Pat. No. 4,795,685.
Prima facie, salts containing iron in the +6 valence state, hereafter called Fe(VI), which are capable of multiple electron reduction, would be capable to provide a higher cathode storage capacity. However, decomposition with reduction of the iron to a less oxidized form (i.e. to a lower valence state) occurs very rapidly, the stability of Fe(VI) salt solutions being only the order of a few hours at room temperature (Anal. Chem. 23, 1312-4, 1951). The Fe(VI) salts may be made by chemical oxidation, such as reported by G. Thompson (J. Amer. Chem, Soc. 73, 1379, 1951), or by precipitation from another Fe(VI) salt, such as reported by J. Gump et al. (Anal. Chem. 26, 1957, 1954). However, as mentioned in a later report by H. Goff et al (J. Amer. Chem, Soc. 93, 6058-6065, 1971), only little is known on the chemistry of Fe(VI) salts. The decomposition of an Fe(VI) salt to a salt in which the iron has a lower valence, results in a spontaneous loss of the electrochemical storage capacity. For example, the anion FeO.sub.4.sup.-2 such as in K.sub.2 FeO.sub.4, is unstable in neutral aqueous solutions and decomposes at a rate k.sub.f according to the following equation: EQU 2FeO.sub.4.sup.2- +3H.sub.2 O.fwdarw.2FeOOH+3/20.sub.2 +4OH.sup.-
The resultant product in this decomposition: Fe(III)OOH, is environmentally more friendly than any of PbO.sub.2, HgO, MnO.sub.2 and NiOOH, but has a lower electrochemical storage capacity.
It is an object of the present invention to provide a novel type of battery which is inexpensive, highly stable, possesses a high storage capacity, a high voltage and is environmentally friendly.